When energy, or the secretion of nervous force, is small, the powers of the man are overtasked by his daily duties, 'his health gives way, and he is soon weeded out of existence by the process of natural selection ; when moderate, it just suffices for the duties and ordinary amusements of his life : he lives, as it were, up to his income, and has nothing to spare. When it is large, he has a surplus to get rid of, or direct, according to his tastes. It may break out in some illegitimate way, or he may utilise it, perhaps in the pursuit of science. It will be seen that the leading scientific men are generally endowed with great energy ; many of the most successful among them have laboured as earnest amateurs in extra-professional hours, working far into the night. They have climbed the long and steep ascent from the lower to the upper ranks of life ; they have learnt where the opportunities of